Dont know if it is the country gentry V London society... more to do with EDMUND being irritated at these artificial social things.. (have posted on this below so wont repeat it)

but I think that he's being silly. Yes there are some silly things about hte "out and not out" stuff, but all the same it did matter. He is just trying to avoid social realities IMO. Being "out" meant that Fanny was eligbile for marriage..and for a girl in her circumstances marriage might really seem the only option for her to avoid poverty. What if Sir T died, suddenly and hadn't left her anything? Tom might also be casual about his obligations to her and she'd end up back home at Portsmouth, and very poor...But of course the Bertrams seem to have decided tacitly that they DONT have any obligation to give Fanny any kind of "social" life or amusement.. without which it is unlikely that she would meet anyone she could marry. SHe is just there to be an unpaid upper servant to Lady B and Mrs N... and I think that Edmund is almost as guilty as the others in ignoring this fact...
Its true that he does get a horse for her, but this is "for her health" rather than for any pleasure he might give her and he then ends up forgettign about her when he can use the horse to court Mary...